Continuous spectra transmission pyrometry

ABSTRACT

An apparatus for processing substrates includes a continuum radiation source, a source manifold optically coupled to the continuum radiation source and comprising: a plurality of beam guides, each having a first end that optically couples the beam guide to the continuum radiation source; and a second end. The apparatus also includes a detector manifold to detect radiation originating from the source manifold and transmitted through a processing area, and one or more transmission pyrometers configured to analyze the source radiation and the transmitted radiation to determine an inferred temperature proximate the processing area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 62/511,620, filed May 26, 2017, which is incorporated herein byreference.

FIELD

Embodiments described herein relate to apparatus and methods ofprocessing substrates. More specifically, apparatus and methodsdescribed herein relate to temperature measurement by radiationtransmission.

BACKGROUND

Transmission pyrometry is a common mode of assessing the thermal stateof a substrate (e.g., a silicon substrate). Thermal processing chamberscommonly expose a substrate to intense, non-coherent or coherentradiation to raise the temperature of the substrate, either of the wholesubstrate or a part or surface area of the substrate. The radiation usedto heat the substrate creates a strong background radiation environmentin the chamber.

High power radiation is used to assess the thermal state of thesubstrate because high power radiation can be differentiated from thebackground radiation in the chamber. Lasers are typically used becauselasers offer high power, and because lasers afford the opportunity toselect a particular wavelength best suited to the substrate. Lasersproduce radiation with a relatively high degree of coherency that, whentransmitted through a substrate, can indicate a thermal state of thesubstrate, which may be registered as a temperature. The transmittedradiation may be detected by a pyrometer, compared to the sourceradiation, and the result correlated to infer the substrate thermalstate. Conventionally, the source radiation is generally selected to beat a small number (e.g., one or two) of narrow wavelength bands. Thetransmitted radiation, likewise, is analyzed only at a small number(e.g., one or two) of narrow wavelength bands

For low temperature applications (e.g., silicon substrate temperaturesbelow about 350° C.), transmission pyrometric measurements may be madereliably by utilizing two primary wavelengths of source radiation.However, for higher temperature applications, the signal-to-noise ratiodegrades. There is a need for reliable transmission pyrometricmeasurements at higher temperatures.

SUMMARY

Embodiments described herein relate to apparatus and methods ofprocessing substrates. More specifically, apparatus and methodsdescribed herein relate to temperature measurement by radiationtransmission.

In an embodiment, a system includes: a continuum radiation source toprovide source radiation; a source manifold optically coupled to thecontinuum radiation source and comprising: a plurality of beam guides,each having a first end that optically couples the beam guide to thecontinuum radiation source; and a second end; a detector manifold todetect radiation originating from the source manifold and transmittedthrough a processing area; and one or more transmission pyrometersconfigured to analyze the source radiation and the transmitted radiationto determine an inferred temperature proximate the processing area.

In an embodiment, a method includes generating source radiation using acontinuum radiation source; directing the source radiation to areceiving surface of a substrate; detecting transmitted radiation froman emitting surface of the substrate, the emitting surface beingopposite of the receiving surface; analyzing the source radiation andthe transmitted radiation to determine an inferred temperature of thesubstrate.

In an embodiment, a method includes constructing a calibration curve fora calibration substrate disposed in a processing chamber bysequentially: heating the calibration substrate to a plurality of knowntemperatures; and measuring a transmitted power spectrum at the knowntemperatures; measuring a test transmitted power spectrum of a testsubstrate at an unknown temperature, wherein the test substrate has asimilar transmission response to the calibration substrate; and usingthe calibration curve and the test transmitted power spectrum to inferthe unknown temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofscope, for the disclosure may admit to other equally effectiveembodiments.

FIG. 1 illustrates an exemplary processing chamber according toembodiments disclosed herein.

FIG. 2 illustrates an exemplary graph of radiation transmitted through asubstrate as a function of wavelength of the radiation.

FIG. 3 illustrates an exemplary method of transmission pyrometryaccording to embodiments disclosed herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Continuous spectra transmission pyrometry (“CSTP”) generally measuresspectra of radiation transmitted through a substrate (e.g., a siliconsubstrate) at a range of wavelengths (more than just one or two primarywavelengths) to infer the temperature of the substrate. CSTP mayreliably measure the temperature, of the substrate at temperatures aboveabout 350° C. In some embodiments, longer wavelengths (e.g., greaterthan 1080 nm) of source radiation may be utilized. It is currentlybelieved that longer wavelengths may allow for higher temperaturemeasurements. By measuring radiation spectra at a range of wavelengths,a redundancy of measurement signals may be created. More redundantsignals may allow for more accurate temperature measurement.

FIG. 1 is a partial perspective diagram of a chamber 300 suitable forCSTP. For example, the chamber 300 may be a rapid thermal processing(RTP) chamber. The chamber 300 generally includes a lamp assembly 310, achamber body 320 and a substrate support assembly 330. For clarity, thechamber 300 has been cross-sectioned, and only the upper portion ofchamber body 320 is illustrated in FIG. 1.

Lamp assembly 310 includes a plurality of lamps 311, each of which ispositioned inside a reflective tube 312. The lamps may be incandescentlamps, such as tungsten-halogen, or other high output lamps, such asdischarge lamps. The reflective tubes 312 are arranged in a honeycombarray 313 inside a water-cooled housing 314. A very thin quartz window315 forms the bottom surface of lamp assembly 310, separating lampassembly 310 from the vacuum usually present in chamber 300. Quartz istypically used for quartz window 315 since quartz is transparent toinfrared light. Lamp assembly 310 is attached to the upper surface ofchamber body 320 in a vacuum-tight manner.

Chamber body 320 includes the walls and floor of chamber 300 as well asa substrate opening 321 and exhaust opening 322. Substrates aredelivered into and removed from chamber 300 through substrate opening321, and a vacuum pump (not shown) evacuates chamber 300 through exhaustopening 322. Slit or gate valves (not shown) may be used to sealsubstrate opening 321 and exhaust opening 322 when necessary.

The substrate support assembly 330 is contained inside chamber body 320and includes an edge ring 331, a rotatable quartz cylinder 332, areflector plate 333 and an array of photo probes 334 (e.g., opticalfibers). Edge ring 331 rests on rotatable quartz cylinder 332. Duringsubstrate processing, edge ring 331 supports the substrate (not shownfor clarity) approximately 25 mm below quartz window 315. Rotatablequartz cylinder 332 may rotates during substrate processing to maximizesubstrate temperature uniformity during processing by minimizing theeffect of thermal asymmetries in chamber 300 on the substrate. Reflectorplate 333 is positioned about 5 mm beneath the substrate. Photo probes334 penetrate reflector plate 333 and are directed at the bottom of thesubstrate during thermal processing. Photo probes 334 transmit radiantenergy from the substrate to one or more pyrometers (e.g., transmissionpyrometer 337) for determining substrate temperature, substratefrontside emissivity, and/or reflectivity during thermal processing. Thepyrometers measure broadband emissions from the backside of thesubstrate in a selected range of wavelengths (e.g., between wavelengthsof about 200 nm to about 5000 nm).

The transmission pyrometer 337 may include a filter that may provide aspectral response sensitive to the wavelength of the absorption gap atthe substrate temperatures between about 100° C. and about 350° C. Theparticular photodetector used therein may be a silicon photodetector fortemperatures below about 350° C., since the absorption gap of siliconvaries from about 1000 nm to about 1200 nm for temperatures from roomtemperature to 350° C. A silicon photodetector may be insensitive toradiation having a wavelength greater than about 1100 nm. Fortemperatures higher than about 350° C., the absorption edge may bebeyond the detection limits of the silicon photodetector, so any furtherincreases in the absorption edge wavelength may not be readily detected.

CSTP generally utilizes a low-divergence, continuum radiation sourcethat generates a wide spectrum of mid-infrared radiation (e.g.,including wavelengths from about 1000 nm to about 1700 nm). The sourcemay emit, or include optics to produce, highly collimated radiation. Thecollimated radiation may be transmitted through a beam guide (e.g., asingle mode optical fiber, a multi-mode optical fiber, etc.) onto asilicon substrate. A portion of the collimated radiation may transmitthrough the substrate. The amplitude of the transmitted radiation may bea function of temperature of the substrate and of the wavelength of thesource radiation. A photo probe (e.g., a light pipe) may be aligned toreceive the transmitted radiation. For example, the photo probe may bealigned with the beam guide.

The photo probe may direct the transmitted radiation to one or morespectrometers. For example, the photo probe may direct the transmittedradiation to a diffraction grating. The diffraction grating may separatethe transmitted radiation in different directions as a function ofwavelength. A collimating lens may focus the diffracted radiation to oneor more focus points. One or more photodetectors may then measure theradiation as a function of direction, which thereby is a function ofwavelength. For example, an indium gallium arsenide linear array may bepositioned at the back focal plane of the collimating lens to measurepower as a function of wavelength. The power spectrum (as a function ofwavelength) of the transmitted radiation may be compared to the powerspectrum of the source radiation. The two power spectra may be used tocalculate the transmission of the substrate as a function of wavelength.This may then be used to infer temperature of the substrate. In someembodiments, zones of the substrate may be identified, and CSTP may bedone on each zone to create a temperature map of the substrate. In someembodiments, longer wavelengths (e.g., greater than 1080 nm) of sourceradiation may be utilized. It is currently believed that longerwavelengths may allow for higher temperature measurements. In someembodiments, a redundancy of measurement signals may be created. Forexample, redundant measurement signals may be created by comparing thepower spectrum of the transmitted radiation to the power spectrum of thesource radiation. More redundant signals may allow for more accuratetemperature measurement.

Inference of temperature from the measured power spectrum of transmittedlight may be aided by calibrating the detector to a known standard. Asubstrate may be heated to a known temperature, and the transmittedpower spectrum recorded at that known temperature. A calibration curvemay be constructed by recording the power spectrum at a plurality ofknown temperatures. The calibration curve can then be used to infer thetemperature of subsequent substrates having the same, or suitablysimilar, transmission responses. Equilibrium and non-equilibriumreadings may be calibrated by controlling the conditions of theequilibrium or non-equilibrium state and relating such conditions to themeasured power spectrum.

As illustrated in FIG. 1, substrate support assembly 330 may define aprocessing area 335, proximate which, during operations, a substrate maybe typically disposed. As illustrated, a continuum radiation source 400is located outside of chamber 300. Other embodiments may have thecontinuum radiation source 400 inside of the lamp assembly 310, attachedto the lamp assembly 310, immediately outside of lamp assembly 310, orotherwise located to suit operational specifications.

The continuum radiation source 400 is configured to generate radiationfor input to source manifold 410. The continuum radiation source 400 maybe a quantum emission source, such as a continuum laser or anappropriately phosphor coated light emitting diode (“LED”), or a highpowered halogen source. The source radiation travels through sourcemanifold 410 and ultimately reaches an incident area of a receivingsurface of the substrate (i.e., proximate the processing area 335). Forexample, source manifold 410 may include a plurality of beam guides 415interspersed with the reflective tubes 312. A collimating lens 420 maybe located at an end of beam guide 415 (i.e., the end closest to theprocessing area 335). The collimating lens 420 may direct the sourceradiation onto an incident area of the receiving surface of thesubstrate. A portion of the source radiation from each beam guide 415may be transmitted from the receiving surface of the substrate to theopposite, emitting surface of the substrate. For example, the sourceradiation may be incident on the receiving surface of the substrate atthe incident area, and the transmitted radiation may exit the emittingsurface of the substrate at the emanating area. The incident area maythus be opposite the emanating area.

A plurality of photo probes 334 may be arranged with an end of eachproximate the emitting surface of the substrate. For example, a photoprobe 334 may be aligned with a beam guide 415 to detect the transmittedradiation. In some embodiments, each beam guide 415 of the sourcemanifold 410 may have an aligned photo probe 334. In other embodiments,there may be more beam guides 415 than photo probes 334. In still otherembodiments, there may be more photo probes 334 than beam guides 415.The collection of photo probes 334 may make up a detector manifold 430.The transmitted radiation may travel through detector manifold 430 andultimately reach one or more transmission pyrometers 337. In someembodiments, a single transmission pyrometer 337 may receive transmittedradiation from all of the photo probes 334. In some embodiments,multiple transmission pyrometers 337 may be utilized. In someembodiments, detector manifold 430 connects a subset of the photo probes334 with each transmission pyrometer 337. In some embodiments, detectormanifold 430 connects a single photo probe 334 with each transmissionpyrometer 337. In some embodiments, detector manifold 430 may utilizeoptical splitters to deliver transmitted radiation from one photo probe334 to multiple transmission pyrometers 337. In some embodiments,detector manifold 430 may utilize optical combiners to delivertransmitted radiation from multiple photo probes 334 to a singletransmission pyrometer 337.

In some embodiments, continuum radiation source 400 may be configured sothat source radiation may be selected over and/or distinguished frombackground radiation. For example, continuum radiation source 400 may bea bright source so that any background radiation is negligible incomparison. As another example, continuum radiation source 400 may beturned off periodically to sample the background radiation forcalibration and/or normalization. In some embodiments, continuumradiation source 400 may be a high-power radiant source, for example aquantum sources such as a laser and/or LED. In some embodiments,continuum radiation source 400 may emit in wavelengths selected tomatch, or otherwise complement, the spectral characteristics of thedetector. In some embodiments, continuum radiation source 400 may be adirected radiation source, for example a collimated or partiallycollimated source, to direct radiation through the substrate to bereceived by the detector. Collimation may be selected to match theradiation to the numerical aperture of the detector. Collimation mayimprove the signal-to-noise ratio of the system.

It should be appreciated that source manifold 410 and/or beam guides 415may be configured to direct source radiation to a plurality of locationsproximate processing area 335 simultaneously or sequentially, as deemedbeneficial to various operation conditions. It should be appreciatedthat source detector manifold 430 and/or photo probes 334 may beconfigured to receive transmitted radiation from a plurality oflocations proximate processing area 335 simultaneously or sequentially,as deemed beneficial to various operation conditions.

The transmission pyrometer 337 may measure the transmitted radiation asa function of wavelength. The power spectrum (as a function ofwavelength) of the transmitted radiation may be compared to the powerspectrum of the source radiation. For example, in some embodiments, thepower spectrum of the source radiation may be obtained directly and/orsimultaneously. In some embodiments, a portion of source manifold 410may be coupled to a portion of detector manifold 430 to provide directmeasurement of the source power spectrum. It should be understood thatsuch measurement may be done simultaneously with, or at about the sametime as, measurements of the power spectrum of the transmittedradiation. The two power spectra may be used to calculate thetransmission of the substrate as a function of wavelength. Thecalculated transmission may then be used to infer temperature of thesubstrate.

FIG. 2 illustrates a graph 700 that compares percent of radiationtransmitted through a substrate as a function of wavelength of theradiation. Line 710 shows the results at a temperature of 25° C. Line720 shows the results at a temperature of 125° C. Line 730 shows theresults at a temperature of 225° C. Line 740 shows the results at atemperature of 325° C. Line 750 shows the results at a temperature of425° C. Line 760 shows the results at a temperature of 525° C. A chamber300 may undergo a calibration procedure that produces data similar tothat of graph 700. Thereafter, a source power spectrum and a transmittedradiation power spectrum may be used with the calibration data to infertemperature of a substrate.

In some embodiments, zones of the substrate may be identified, and CSTPmay be done on each zone to create a temperature map of the substrate.For example, source manifold 410, beam guides 415, detector manifold430, and/or photo probes 334 may be configured to measures spectra ofradiation transmitted through processing area 335 simultaneously orsequentially, as deemed beneficial to various operation conditions. Insome embodiments, longer wavelengths (e.g., greater than 1080 nm) ofsource radiation may be utilized. It is currently believed that longerwavelengths may allow for higher temperature measurements. In someembodiments, a redundancy of measurement signals may be created. Forexample, redundant measurement signals may be created by comparing thepower spectrum of the transmitted radiation to the power spectrum of thesource radiation. More redundant signals may allow for more accuratetemperature measurement.

A method 800 of transmission pyrometry is illustrated in FIG. 3. Asillustrated, the method 800 begins at block 810, wherein sourceradiation is generated with a continuum source. In some embodiments, thesource radiation includes a spectrum from visible to mid-infrared. Insome embodiments, the source radiation spectrum includes wavelengthsfrom about 1000 nm to about 1700 nm. The method 800 continues at block820 wherein the source radiation is directed at a substrate, such as asilicon substrate. For example the source radiation may be directed at areceiving surface of the substrate.

The method 800 continues at block 830 wherein transmitted radiation isdetected from the substrate. For example the transmitted radiation maybe detected from an emitting surface of the silicon substrate. Thereceiving surface and the transmitting surface may be on opposite sidesof the silicon substrate. The method continues at block 840 wherein thesource radiation and the transmitted radiation are analyzed. Forexample, the source radiation and the transmitted radiation may beanalyzed to determine an inferred temperature of the substrate. In someembodiments, the method continues at block 842 wherein analyzing thesource radiation and the transmitted radiation includes measuring poweras a function of wavelength of the transmitted radiation. In someembodiments, as shown at block 844, at least one spectrometer is used tomeasure power as a function of wavelength of the transmitted radiation.In some embodiments, the method continues from block 840 to block 846,and an inferred temperature of a plurality of zones of the substrate isdetermined.

What is claimed is:
 1. A system comprising: a continuum radiation sourceto provide source radiation; a source manifold optically coupled to thecontinuum radiation source and comprising: a plurality of beam guides,each having a first end that optically couples the beam guide to thecontinuum radiation source; and a second end; a detector manifold todetect radiation originating from the source manifold and transmittedthrough a processing area; and one or more transmission pyrometersconfigured to analyze the source radiation and the transmitted radiationto determine an inferred temperature proximate the processing area. 2.The system of claim 1, wherein the detector manifold comprises: aplurality of pyrometer probes, each having a first end to receive thetransmitted radiation and a second end; and a diffraction grating at thesecond end of each pyrometer probe.
 3. The system of claim 2, whereinthe first ends of the plurality of pyrometry probes are distributedacross the processing area.
 4. The system of claim 1, wherein: thesecond ends of the plurality of beam guides are distributed across theprocessing area; the detector manifold comprises a plurality ofpyrometer probes, each having a third end to receive the transmittedradiation and a fourth end; the third ends of the plurality of pyrometryprobes are distributed across the processing area; and at least one ofthe second ends aligns with at least one of the third ends.
 5. Thesystem of claim 1, wherein at least one of the transmission pyrometersis configured to measure power as a function of wavelength of thetransmitted radiation.
 6. The system of claim 5, wherein the at leastone of the transmission pyrometers comprises a spectrometer.
 7. Thesystem of claim 5, wherein the at least one of the transmissionpyrometers comprises: a diffraction grating; a cylinder lens; and anindium gallium arsenide linear detector array.
 8. The system of claim 1,wherein the detector manifold comprises at least one of an opticalsplitter and an optical combiner.
 9. The system of claim 1, wherein thedetector manifold comprises a plurality of pyrometer probes, thetransmission pyrometer comprising a spectrometer for each of thepyrometer probes.
 10. The system of claim 1, wherein the continuumradiation source has an emission spectrum from visible to mid-infrared.11. The system of claim 10, wherein the emission spectrum compriseswavelengths from about 1000 nm to about 1700 nm.
 12. The system of claim1, wherein the continuum radiation source is a quantum emission source.13. The system of claim 1, wherein: the detector manifold comprises aplurality of pyrometer probes, each having a third end and a fourth endcoupled to the one or more transmission pyrometers; and the second endof at least one of the beam guides is directly coupled to the third endof at least one of the pyrometry probes without passing through theprocessing area.
 14. A method comprising: generating source radiationusing a continuum radiation source; directing the source radiation to areceiving surface of a substrate; detecting transmitted radiation froman emitting surface of the substrate, the emitting surface beingopposite of the receiving surface; and analyzing the source radiationand the transmitted radiation to determine an inferred temperature ofthe substrate.
 15. The method of claim 14, wherein the analyzing thesource radiation and the transmitted radiation comprises measuring poweras a function of wavelength of the transmitted radiation.
 16. The methodof claim 15, wherein at least one spectrometer is used to measure poweras a function of wavelength of the transmitted radiation.
 17. The methodof claim 14, wherein the source radiation comprises a spectrum fromvisible to mid-infrared.
 18. The method of claim 17, wherein the sourceradiation spectrum comprises wavelengths from about 1000 nm to about1700 nm.
 19. The method of claim 14, wherein the emitting surface of thesubstrate is identified by a plurality of zones, the method furthercomprising determining an inferred temperature of each of the pluralityof zones of the substrate.
 20. A method comprising: constructing acalibration curve for a calibration substrate disposed in a processingchamber by sequentially: heating the calibration substrate to aplurality of known temperatures; and measuring a transmitted powerspectrum at the known temperatures; measuring a test transmitted powerspectrum of a test substrate at an unknown temperature, wherein the testsubstrate has a similar transmission response to the calibrationsubstrate; and using the calibration curve and the test transmittedpower spectrum to infer the unknown temperature.